The used lunch trays Emily Fox took home about four years ago from the loading dock outside her elementary school were gross, some still plastered with ketchup. Emily stacked the trays in piles of 10. She wanted to know just how many polystyrene lunch trays Piney Branch Elementary School students went through in a day.

“Three hundred and twenty-five,” said Emily, now 12 and a middle-school student. “And they all go into the incinerator and get burned and it’s very unenvironmental.”

For more than four years, Emily and other members of the Young Activist Club in Maryland’s Montgomery County have been asking the Board of Education for a dishwasher at Piney Branch. They want to phase out foam for something greener, but their lobbying and fundraising, which has netted more than $10,000, have yielded little success.

From Maryland to Illinois to California, environmentally minded students are pushing to remove polystyrene trays from cafeterias and replace them with compostable, reusable or recyclable alternatives. But change has been slow.

School districts say that they want to go foam-free but that tight education budgets, infrastructure limitations and the relatively high prices of earth-friendly materials are often insurmountable hurdles in difficult economic times.

Even in Portland, one of the greenest cities in America, some schools still serve lunches on styrene-based, disposable trays.

“I hate serving on Styrofoam, but when push comes to shove, you have to decide where you’re going to spend the money,” said Gitta Grether-Sweeney, director of nutrition services for Portland Public Schools.

For decades, environmentalists have shunned polystyrene (better known by the name of Dow Chemical’s trademarked Styrofoam) because it is slow to biodegrade and litters oceans and landfills.

Corporations and municipalities have taken note. McDonald’s stopped using foam burger boxes about 20 years ago. Jamba Juice plans to replace foam cups with paper ones nationally by the end of 2013. And hundreds of cities and towns have passed laws banning polystyrene food containers.

But change has been spotty for the nation’s school systems.

“We tend to be very resistant to change,” said David Binkle, director of food services for the Los Angeles Unified School District. Los Angeles Unified, the second-largest public-school district in the nation, switched to compostable paper trays in August. The change got national attention after middle-school activists strung up a 30-foot tower of foam trays in a tree to spotlight the waste.

On Friday, the Hermosa Beach City School District in Southern California started replacing foam trays with recycled paper trays once a week, thanks in part to the advocacy of Max Riley, a fourth-grader at Hermosa Valley School, and his second-grader sister, Reece.

“No Foam Friday” will run through the end of the school year, and the siblings say they’re pushing for permanent change.

Max said he worries about the health repercussions of littering the Earth with foam.

Across the country, student activists have rallied to get foam lunch trays out of schools because “our young people care about the planet they’re going to have to inhabit,” said Dawn Undurraga, a nutritionist with the Environmental Working Group.

“You have 31.8 million children in the school-lunch program each day, and multiply that by 180 school days and that comes out to quite a bit of trays if they’re all disposable,” Undurraga said.

But even young Max knows that there are economic realities to consider.

“Foam is very popular because it’s really cheap,” Max said. “And 3 cents extra per tray doesn’t sound like much, but in the big scheme, it is thousands of dollars, which I don’t really mind but a lot of people do.”

Grades of Green, a nonprofit group, seeks to empower students such as Max to make positive environmental changes, and it has helped more than 150 schools in 25 states implement policies that make campuses greener.

The Portland school system spends about 7 cents each for paper trays, compared with 3 cents for foam trays.

But making the switch doesn’t always cost more.

In 2010, the New York City Department of Education implemented “Trayless Tuesdays.” Officials estimated that the move diverted 2.4 million polystyrene trays from landfills each month and was cost-neutral.

Binkle said the Los Angeles district negotiated with suppliers when it moved away from foam, saving the school system at least $1 million on the 120 million lunch trays students use annually.

Trays made from recyclable materials can end up in landfills if composting facilities are not available on site, as is the case at some Portland and Los Angeles schools. And students have to be trained to clean trays, which can’t be recycled if contaminated with bits of food or grease.

That’s why the Young Activist Club at Piney Branch doesn’t want anything but reusable trays and a dishwasher.